TEAS Science: Chemistry and Physical Science 1 — Questions and Answers

Question 1: What is the pH of a neutral solution at 25°C?

0
5
7 (Correct answer)
14

Correct answer: 7

A neutral solution has a pH of 7, where the concentration of hydrogen ions (H⁺) equals the concentration of hydroxide ions (OH⁻).

The pH scale measures the concentration of hydrogen ions (H⁺) in solution: pH = -log[H⁺]. At pH 7, [H⁺] = [OH⁻] = 10⁻⁷ mol/L — the solution is neutral. pH < 7 is acidic (more H⁺ than OH⁻); pH > 7 is basic/alkaline (more OH⁻ than H⁺). In the human body: blood pH is 7.35–7.45 (slightly alkaline); stomach acid is pH ~1–2; urine is pH ~4.5–8.0. Maintaining blood pH within this narrow range is critical — acidosis (pH < 7.35) and alkalosis (pH > 7.45) are medical emergencies.

Question 2: Which of the following best describes an acid according to the Brønsted-Lowry definition?

A substance that accepts protons (H⁺)
A substance that donates protons (H⁺) (Correct answer)
A substance that accepts electrons
A substance that donates hydroxide ions (OH⁻)

Correct answer: A substance that donates protons (H⁺)

In the Brønsted-Lowry theory, an acid is a proton (H⁺) donor — it releases H⁺ ions in solution.

There are three common definitions of acids: (1) Arrhenius: acids produce H⁺ (or H₃O⁺) in water, bases produce OH⁻; (2) Brønsted-Lowry: acids are proton (H⁺) donors, bases are proton acceptors; (3) Lewis: acids are electron-pair acceptors, bases are electron-pair donors. For TEAS purposes, the Arrhenius and Brønsted-Lowry definitions are most relevant. Examples: HCl donates H⁺ (acid); NaOH produces OH⁻ (Arrhenius base) and accepts H⁺ (Brønsted base). Strong acids completely dissociate in water (HCl, HNO₃, H₂SO₄); weak acids partially dissociate (acetic acid).

Question 3: In a chemical equation, what does the law of conservation of mass require?

Products must weigh more than reactants
The number of atoms of each element must be equal on both sides of the equation (Correct answer)
Reactions always release energy
Products must be simpler than reactants

Correct answer: The number of atoms of each element must be equal on both sides of the equation

The law of conservation of mass states that matter cannot be created or destroyed — the total mass and number of atoms of each element must be the same on both sides of a chemical equation.

Lavoisier's law of conservation of mass: in a chemical reaction, matter is neither created nor destroyed — only rearranged. Therefore, in a balanced equation, the number of atoms of each element must be identical on the reactant and product sides. For example, in 2H₂ + O₂ → 2H₂O: Reactant side: 4 H atoms + 2 O atoms. Product side: 4 H atoms + 2 O atoms. Balanced. Coefficients (the numbers before chemical formulas) are adjusted to achieve balance — subscripts (part of the formula) cannot be changed without altering the compound's identity.

Question 4: Which of the following best describes a physical change?

Iron rusting when exposed to oxygen and water
Water boiling and turning to steam (Correct answer)
Wood burning in a fireplace
Milk souring after being left out

Correct answer: Water boiling and turning to steam

Water boiling is a physical change — the chemical composition (H₂O) does not change, only the physical state (liquid to gas).

Physical changes: alter the form or appearance of a substance without changing its chemical composition. Examples: melting, freezing, boiling, condensing, cutting, dissolving, mixing. Chemical changes: alter the chemical composition, creating new substances with different properties. Evidence of chemical change: color change, gas production, precipitate formation, temperature change, light emission. Option B (boiling) — H₂O changes state from liquid to gas but remains H₂O (physical). Options A (rusting = Fe₂O₃ formed), C (combustion), and D (fermentation/acid production) are all chemical changes.

Question 5: What is the atomic number of an element?

The total number of protons and neutrons in the nucleus
The number of protons in the nucleus of an atom (Correct answer)
The number of electrons in the outermost shell
The average atomic mass of the element

Correct answer: The number of protons in the nucleus of an atom

The atomic number (Z) is the number of protons in the nucleus, which uniquely identifies the element and determines its position on the periodic table.

Atomic structure: The atomic number (Z) = number of protons in the nucleus. It is unique to each element (e.g., Hydrogen Z=1, Carbon Z=6, Oxygen Z=8). In a neutral atom, number of protons = number of electrons. The mass number (A) = protons + neutrons. Isotopes: same element (same Z) but different numbers of neutrons (different mass numbers). For example, Carbon-12 and Carbon-14 both have 6 protons but different neutron counts (6 vs. 8). Ions: atoms that have gained (anions) or lost (cations) electrons, acquiring a charge.

Question 6: Which type of chemical bond involves the sharing of electrons between atoms?

Ionic bond
Covalent bond (Correct answer)
Metallic bond
Hydrogen bond

Correct answer: Covalent bond

Covalent bonds form when atoms share pairs of electrons, commonly between nonmetal atoms.

Types of chemical bonds: (1) Covalent bonds — atoms share electron pairs; typically between nonmetals; can be nonpolar (equal sharing, e.g., H₂, O₂) or polar (unequal sharing, e.g., H₂O, HCl). (2) Ionic bonds — one atom transfers electrons to another; between metals and nonmetals; result in ions (e.g., NaCl: Na⁺ and Cl⁻). (3) Metallic bonds — electrons delocalized in a 'sea' of electrons in metals. (4) Hydrogen bonds — weak attractions between H bonded to N/O/F and another electronegative atom — not true chemical bonds but very important in biology (DNA base pairs, protein structure, water properties).

Question 7: When a patient receives an IV solution of normal saline (0.9% NaCl), which type of solution is this relative to normal blood plasma?

Hypotonic solution
Hypertonic solution
Isotonic solution (Correct answer)
Supersaturated solution

Correct answer: Isotonic solution

Normal saline (0.9% NaCl) is isotonic to blood plasma — it has the same solute concentration as blood, preventing osmotic shifts in red blood cells.

Tonicity describes how a solution's solute concentration compares to the inside of a cell: Isotonic (same concentration as cell) — cells neither shrink nor swell; 0.9% NaCl and 5% dextrose are isotonic to blood. Hypotonic (lower concentration than cell) — water enters cells, causing swelling and potential lysis; 0.45% NaCl is hypotonic. Hypertonic (higher concentration than cell) — water leaves cells, causing shrinkage (crenation in RBCs); 3% NaCl is hypertonic. Normal saline (0.9% NaCl) is the most commonly used isotonic IV fluid, used to restore blood volume without changing the tonicity of body fluids.

Question 8: Which of the following statements about enzymes is TRUE?

Enzymes are consumed in the reactions they catalyze.
Enzymes are denatured and permanently destroyed at 37°C.
Enzymes lower the activation energy required for a chemical reaction. (Correct answer)
Enzymes can only catalyze reactions in acidic conditions.

Correct answer: Enzymes lower the activation energy required for a chemical reaction.

Enzymes are biological catalysts that lower the activation energy needed for a reaction, allowing it to proceed faster without being consumed in the process.

Enzyme properties: (1) Catalysts — not consumed, can be reused; (2) Lower activation energy (not provide energy); (3) Highly specific — each enzyme has an active site that fits its substrate(s) like a lock and key (or induced fit model); (4) Affected by temperature and pH — optimal conditions vary by enzyme (most human enzymes optimal at ~37°C and pH ~7); (5) Denatured (lose shape and function) at high temperatures or extreme pH; (6) Speed both forward and reverse reactions proportionally — do not change equilibrium constants. Inhibitors (competitive/non-competitive) can reduce enzyme activity.

Question 9: What is the difference between an element and a compound?

An element is a mixture; a compound is a pure substance
An element contains only one type of atom; a compound contains two or more elements chemically bonded together (Correct answer)
Elements can be separated by physical means; compounds cannot be separated at all
A compound has fewer atoms than an element

Correct answer: An element contains only one type of atom; a compound contains two or more elements chemically bonded together

An element is a pure substance consisting of only one type of atom (e.g., oxygen O₂). A compound is a pure substance formed when two or more different elements are chemically bonded in fixed proportions (e.g., water H₂O).

Classification of matter: Pure substances have uniform composition — either elements (one type of atom, e.g., Fe, O₂, Au) or compounds (two+ elements chemically bonded, e.g., H₂O, NaCl, CO₂). Mixtures contain two or more substances not chemically bonded — either homogeneous (uniform, e.g., saltwater) or heterogeneous (non-uniform, e.g., salad). Key distinction for compounds: elements combine in fixed, definite proportions by mass (Proust's law of definite proportions). H₂O is always 2:1 H to O by atom count. Compounds can be separated into elements only by chemical means (not physical).

Question 10: Which of the following correctly describes the relationship between the frequency and wavelength of electromagnetic radiation?

Frequency and wavelength are directly proportional; as wavelength increases, frequency increases
Frequency and wavelength are inversely proportional; as wavelength increases, frequency decreases (Correct answer)
Frequency and wavelength are unrelated
Both frequency and wavelength decrease as energy increases

Correct answer: Frequency and wavelength are inversely proportional; as wavelength increases, frequency decreases

Frequency (ν) and wavelength (λ) are inversely proportional: ν = c/λ, where c is the speed of light. As wavelength increases, frequency decreases, and vice versa.

Electromagnetic radiation: The wave equation is c = λν, where c = speed of light (3 × 10⁸ m/s), λ = wavelength (m), ν = frequency (Hz). Since c is constant, λ and ν are inversely proportional. Electromagnetic spectrum from low to high frequency (high to low wavelength): Radio waves → Microwaves → Infrared → Visible light → Ultraviolet → X-rays → Gamma rays. Energy is directly proportional to frequency (E = hν). Medical applications: X-rays and gamma rays have high frequency/energy/low wavelength — used in imaging and radiation therapy. Understanding electromagnetic properties is relevant for radiation safety in healthcare settings.

Question 11: In chemistry, what is a solution?

A heterogeneous mixture where components can be visually distinguished
A homogeneous mixture in which a solute is uniformly dissolved in a solvent (Correct answer)
A pure substance composed of a single element
A reaction that produces a precipitate

Correct answer: A homogeneous mixture in which a solute is uniformly dissolved in a solvent

A solution is a homogeneous mixture where a solute (dissolved substance) is uniformly distributed throughout a solvent (dissolving medium), such as salt dissolved in water.

A solution consists of: Solute — the substance dissolved (present in smaller amount); Solvent — the dissolving medium (present in larger amount). In saline: NaCl is the solute, water is the solvent. Properties of solutions: Homogeneous — uniform composition throughout; Solute is dispersed at the molecular/ionic level; Stable — does not settle; Clear (may be colored). Compared to other mixtures: Suspension (particles >1000 nm, heterogeneous, settles) and Colloid (particles 1–1000 nm, appears homogeneous but particles don't settle). Blood is a colloid. IV solutions are true solutions. Concentration can be expressed as percent, molarity (M), or mg/dL.

Question 12: What happens during an exothermic chemical reaction?

Energy is absorbed from the surroundings, causing the system to cool
Energy is released to the surroundings, causing the system to warm (Correct answer)
No energy transfer occurs between the system and the surroundings
The reaction requires a constant energy input to continue

Correct answer: Energy is released to the surroundings, causing the system to warm

In an exothermic reaction, the products have less energy than the reactants, so the energy difference is released to the surroundings as heat, light, or other forms.

Thermochemistry: Exothermic reactions release energy (ΔH < 0, negative enthalpy change). The reactants have more energy than the products — the difference is released as heat (and sometimes light). Examples: combustion (burning), cellular respiration (glucose oxidation), neutralization (acid + base). The surroundings warm up. Endothermic reactions absorb energy (ΔH > 0, positive enthalpy change). The products have more energy than the reactants. Examples: photosynthesis, dissolving ammonium nitrate (instant cold packs). The surroundings cool down. In biology, cellular respiration (C₆H₁₂O₆ + O₂ → CO₂ + H₂O + energy) is exothermic — this energy is captured in ATP.

Question 13: Which of the following is an example of a chemical property?

The density of gold is 19.3 g/cm³
Water freezes at 0°C
Hydrogen gas is highly flammable (Correct answer)
Iron has a shiny metallic luster

Correct answer: Hydrogen gas is highly flammable

Flammability describes how a substance reacts with oxygen (a chemical change) — this is a chemical property. The others describe physical properties observed without changing the substance.

Physical properties: observable without changing chemical composition — density, color, luster, melting/boiling point, hardness, malleability, conductivity, state of matter. Chemical properties: describe a substance's ability to undergo chemical changes — flammability (reacts with O₂), reactivity with acids, tendency to oxidize (rust), toxicity, radioactive decay. Option C (flammability) requires H₂ to undergo combustion (2H₂ + O₂ → 2H₂O) — a chemical reaction changing its composition. Options A (density), B (freezing point), and D (luster) are all physical properties observed without chemical change.

Question 14: In the context of nuclear science, what is radioactive decay?

A process where atoms gain electrons to become stable
A process where an unstable nucleus spontaneously emits particles or energy to become more stable (Correct answer)
A process where electrons fall to lower energy levels, emitting light
A process where molecules break apart due to heat

Correct answer: A process where an unstable nucleus spontaneously emits particles or energy to become more stable

Radioactive decay is the spontaneous emission of particles or energy from an unstable atomic nucleus as it transforms into a more stable configuration.

Radioactive decay occurs when an atomic nucleus is unstable (often due to an imbalance in the neutron-to-proton ratio or excess energy). Types of decay: Alpha decay (emits helium nucleus: 2 protons + 2 neutrons — low penetration, stopped by paper); Beta decay (emits electron or positron — moderate penetration, stopped by aluminum); Gamma decay (emits high-energy photons — high penetration, requires lead/thick concrete shielding). Medical applications: PET scans (positron emission), radiotherapy (gamma radiation to kill tumors), diagnostic imaging (technetium-99m), and carbon-14 dating (in forensics/archaeology). Half-life determines the decay rate and dosing intervals in nuclear medicine.

Question 15: What is the difference between a cation and an anion?

Cations are negatively charged; anions are positively charged
Cations are positively charged (lost electrons); anions are negatively charged (gained electrons) (Correct answer)
Cations have more neutrons; anions have more protons
Cations are nonmetals; anions are metals

Correct answer: Cations are positively charged (lost electrons); anions are negatively charged (gained electrons)

Cations form when an atom loses electrons (becoming positively charged); anions form when an atom gains electrons (becoming negatively charged).

Ions form when atoms gain or lose electrons: Cations (+) — formed when an atom loses one or more electrons; metals commonly form cations (e.g., Na⁺, Ca²⁺, K⁺, Fe³⁺). Anions (-) — formed when an atom gains one or more electrons; nonmetals commonly form anions (e.g., Cl⁻, O²⁻, S²⁻, PO₄³⁻). Ionic compounds form when cations and anions attract electrostatically (e.g., NaCl = Na⁺ + Cl⁻). In the body: electrolytes are ions critical for nerve impulse transmission, muscle contraction, and fluid balance. Key cations: Na⁺, K⁺, Ca²⁺, Mg²⁺. Key anions: Cl⁻, HCO₃⁻, PO₄³⁻.

Question 16: Which of the following correctly describes the behavior of molecules during diffusion?

Molecules move from areas of low concentration to high concentration
Molecules move from areas of high concentration to low concentration (Correct answer)
Molecules remain stationary unless actively transported
Molecules only move when temperature is below 37°C

Correct answer: Molecules move from areas of high concentration to low concentration

During diffusion, molecules move randomly but the net movement is from areas of high concentration to low concentration, down the concentration gradient, until equilibrium is reached.

Diffusion is the net movement of molecules from high to low concentration — down the concentration gradient — due to random thermal motion. It is a passive process requiring no energy. Diffusion continues until equilibrium is reached (equal concentrations on both sides). Rate of diffusion is affected by: temperature (higher temperature = faster movement), concentration gradient (steeper gradient = faster diffusion), molecular size (smaller molecules diffuse faster), and distance. In the body: O₂ diffuses from alveoli (high O₂) into blood (lower O₂); CO₂ diffuses from blood (high CO₂) into alveoli (lower CO₂). Fick's law describes quantitative diffusion rates.

Question 17: Which of Newton's laws states that an object in motion stays in motion unless acted upon by an external force?

Newton's First Law (Law of Inertia) (Correct answer)
Newton's Second Law (F = ma)
Newton's Third Law (Action-Reaction)
Newton's Law of Universal Gravitation

Correct answer: Newton's First Law (Law of Inertia)

Newton's First Law (Law of Inertia) states that an object will remain in its current state of motion (rest or constant velocity) unless acted upon by a net external force.

Newton's Three Laws of Motion: First Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless a net external force acts on it. Second Law: F = ma (Force = mass × acceleration) — the net force on an object equals its mass times acceleration. Third Law (Action-Reaction): For every action, there is an equal and opposite reaction. Physical science applications in healthcare: understanding forces during patient transfers/positioning (preventing injury), CPR physics, biomechanics of body movement, and how IV flow rates relate to pressure and gravity.

Question 18: The atomic mass of carbon is approximately 12 amu. What does this value represent?

The number of protons in the carbon nucleus
The number of electrons in a carbon atom
The weighted average mass of naturally occurring carbon isotopes (Correct answer)
The number of neutrons in carbon-12

Correct answer: The weighted average mass of naturally occurring carbon isotopes

Atomic mass is the weighted average of the masses of all naturally occurring isotopes of an element, taking into account their relative abundances.

Atomic mass (average atomic mass) is NOT the mass of a single atom — it is the weighted average of the masses of all naturally occurring stable isotopes of an element, each weighted by its natural abundance. Carbon has two main stable isotopes: Carbon-12 (98.9% abundant, mass = 12 amu) and Carbon-13 (1.1% abundant, mass = 13 amu). Weighted average: (0.989 × 12) + (0.011 × 13) ≈ 12.011 amu. Carbon's atomic number is 6 (protons), which is separate from atomic mass. The mass number (12 or 13) = protons + neutrons for a specific isotope.

Question 19: Which state of matter has definite volume but no definite shape?

Solid
Liquid (Correct answer)
Gas
Plasma

Correct answer: Liquid

A liquid has a definite volume but takes the shape of its container — it has no definite shape. Solids have both definite shape and volume; gases have neither.

States of matter properties: Solid — definite shape AND definite volume (particles tightly packed in fixed positions, strong intermolecular forces); Liquid — definite volume, NO definite shape (particles close together but can flow past each other, moderate intermolecular forces); Gas — NO definite shape, NO definite volume (particles widely spread, move rapidly, weak intermolecular forces, fill available space); Plasma — ionized gas (high energy state, found in stars and lightning). Phase transitions involve energy: melting (solid→liquid), vaporization/boiling (liquid→gas), sublimation (solid→gas), freezing, condensation, deposition.

Question 20: Which of the following best describes the scientific method?

A series of rigid, infallible steps guaranteed to produce correct results
A systematic process of observation, hypothesis formation, experimentation, and conclusion to investigate natural phenomena (Correct answer)
A method used only by professional scientists in laboratories
A method of learning through reading textbooks and memorizing facts

Correct answer: A systematic process of observation, hypothesis formation, experimentation, and conclusion to investigate natural phenomena

The scientific method is a systematic approach to investigation involving observation, hypothesis, testing, data collection, analysis, and conclusion — it is iterative and self-correcting.

Scientific method steps: (1) Observation — notice a phenomenon; (2) Question — what causes it?; (3) Hypothesis — a testable, falsifiable explanation; (4) Experiment — controlled test to gather data; (5) Data analysis — interpret results; (6) Conclusion — does data support or refute the hypothesis?; (7) Communication and peer review; (8) Replication. Key features: hypotheses must be falsifiable; experiments use controlled variables (independent variable changed, dependent variable measured, controlled variables held constant); the method is self-correcting (new evidence can revise conclusions). Scientific knowledge is never 'proven' absolutely — it represents the best current explanation of available evidence.

Question 21: In which of the following situations is a buffer solution most important?

In distilled water used for rinsing equipment
In maintaining the pH of blood within the narrow range of 7.35–7.45 (Correct answer)
In preparing concentrated acid solutions
In creating hypertonic IV solutions

Correct answer: In maintaining the pH of blood within the narrow range of 7.35–7.45

Blood contains bicarbonate and other buffer systems that resist pH changes, maintaining the critical 7.35–7.45 range necessary for normal enzyme function and cellular processes.

A buffer solution resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base (or weak base + conjugate acid). Blood buffer systems: (1) Bicarbonate buffer (most important): CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻; regulated by lungs (CO₂ elimination) and kidneys (HCO₃⁻ excretion/retention); (2) Protein buffers (hemoglobin, plasma proteins); (3) Phosphate buffer (important in urine and intracellular fluid). Acidosis (pH < 7.35) and alkalosis (pH > 7.45) are medical emergencies that impair enzyme function, oxygen transport, and cellular processes.

Question 22: Which of the following molecules is non-polar?

Water (H₂O)
Ammonia (NH₃)
Carbon dioxide (CO₂) (Correct answer)
Hydrogen chloride (HCl)

Correct answer: Carbon dioxide (CO₂)

CO₂ is a linear molecule with two equal and opposite C=O dipoles that cancel out, resulting in a net dipole moment of zero — making it nonpolar overall.

Polarity depends on both bond polarity and molecular geometry. A molecule is nonpolar if: (a) all bonds are nonpolar (e.g., O₂, N₂, H₂), OR (b) it has polar bonds but they are symmetrically arranged and cancel (e.g., CO₂: linear, O=C=O, dipoles cancel; CCl₄: tetrahedral). CO₂ is linear — both C=O bonds are identical and point in opposite directions, so dipoles cancel → nonpolar. H₂O is polar (bent/V-shape geometry — dipoles don't cancel). NH₃ is polar (trigonal pyramidal — dipoles add up). HCl is polar (diatomic, different atoms). Polarity affects solubility: 'like dissolves like' — polar solvents dissolve polar solutes.

Question 23: What is the name for the minimum amount of energy required to start a chemical reaction?

Heat of reaction
Enthalpy change
Activation energy (Correct answer)
Free energy

Correct answer: Activation energy

Activation energy is the minimum energy required for reactant molecules to overcome the energy barrier and successfully react to form products.

Activation energy (Ea) is the minimum energy that colliding reactant molecules must have for a reaction to occur. On an energy diagram (reaction coordinate diagram): the y-axis is potential energy, the x-axis is reaction progress. Reactants must 'climb' the energy barrier (activation energy) to reach the transition state before descending to products. Key points: Catalysts (including enzymes) lower Ea, increasing reaction rate WITHOUT changing the energy of reactants or products or the overall energy change (ΔH). Higher temperature provides more molecules with energy ≥ Ea, increasing reaction rate. Inhibitors can raise Ea or block active sites.

Question 24: Which of the following correctly describes what happens during ionization?

An atom gains protons to become a different element
An atom or molecule loses or gains electrons to become a charged particle (ion) (Correct answer)
Atoms share electrons to form covalent bonds
A molecule is broken down by adding water

Correct answer: An atom or molecule loses or gains electrons to become a charged particle (ion)

Ionization is the process by which an atom or molecule loses or gains electrons, creating a charged particle called an ion.

Ionization: In chemistry, ionization occurs when an atom or molecule gains or loses one or more electrons, creating an ion. Losing electrons → cation (positive charge); Gaining electrons → anion (negative charge). Ionization energy (first IE) is the energy required to remove the outermost electron from a neutral atom in the gas phase. In solutions (like body fluids): ionic compounds like NaCl dissociate into Na⁺ and Cl⁻ ions. Strong electrolytes fully ionize (HCl, NaCl); weak electrolytes partially ionize (acetic acid). Ionizing radiation (X-rays, gamma rays, alpha/beta particles) can ionize atoms in body tissues, potentially damaging DNA.

Question 25: In a chemical reaction, if the reactants are hydrogen gas (H₂) and oxygen gas (O₂), which of the following balanced equations correctly represents the formation of water?

H₂ + O₂ → H₂O
2H₂ + O₂ → 2H₂O (Correct answer)
H₂ + 2O₂ → H₂O₂
4H₂ + O₂ → 4H₂O

Correct answer: 2H₂ + O₂ → 2H₂O

The balanced equation 2H₂ + O₂ → 2H₂O has 4 H atoms and 2 O atoms on each side, satisfying conservation of mass.

Balancing 2H₂ + O₂ → 2H₂O: Reactant side: 2×2 = 4 H atoms; 1×2 = 2 O atoms. Product side: 2×2 = 4 H atoms; 2×1 = 2 O atoms. Balanced! ✓ Option A (H₂ + O₂ → H₂O): 2H + 2O → 2H + 1O — unbalanced. Option C creates H₂O₂ (hydrogen peroxide), a different compound. Option D (4H₂ + O₂ → 4H₂O): 8H + 2O → 8H + 4O — unbalanced. When balancing, adjust coefficients (numbers before formulas), NEVER subscripts (part of the chemical formula). This is the synthesis of water, one of the most important chemical reactions.

Question 26: What does a catalyst do in a chemical reaction?

It increases the activation energy of the reaction
It is consumed in the reaction, providing energy to reactants
It speeds up the reaction by providing an alternative pathway with lower activation energy (Correct answer)
It changes the equilibrium position, favoring product formation

Correct answer: It speeds up the reaction by providing an alternative pathway with lower activation energy

A catalyst provides an alternative reaction pathway with lower activation energy, increasing the reaction rate without being consumed or changing the overall energy of reactants/products.

Catalysts function by: (1) Providing an alternative reaction mechanism with lower activation energy (Ea); (2) NOT being consumed — they are regenerated at the end and can be reused; (3) NOT changing the thermodynamics (ΔG, ΔH) — they don't change whether a reaction is spontaneous or the equilibrium position; (4) Increasing both forward and reverse reaction rates equally. In biology, enzymes are protein catalysts essential for life — they make reactions occur at body temperature that would otherwise require extremely high temperatures. Industrial catalysts: catalytic converters in cars, Haber process for ammonia synthesis.

Question 27: A solution with a pH of 3 compared to a solution with a pH of 5 is:

10 times more basic
100 times more acidic (Correct answer)
10 times more acidic
2 times more acidic

Correct answer: 100 times more acidic

The pH scale is logarithmic — each unit difference represents a 10-fold difference in hydrogen ion concentration. A difference of 2 pH units = 10² = 100-fold difference.

The pH scale is logarithmic: pH = -log[H⁺]. Each 1-unit decrease in pH = 10-fold increase in [H⁺]. For pH 3 vs. pH 5: difference = 5 - 3 = 2 units. Difference in [H⁺] = 10² = 100 times. pH 3 has [H⁺] = 10⁻³ mol/L; pH 5 has [H⁺] = 10⁻⁵ mol/L. Ratio: 10⁻³/10⁻⁵ = 10² = 100. Therefore, pH 3 is 100 times MORE acidic (more H⁺) than pH 5. Clinical significance: stomach acid (pH 1–2) is approximately 1,000–100,000 times more acidic than blood (pH 7.4). The narrow blood pH range of 7.35–7.45 represents only about a 1.26-fold change in [H⁺], yet is life-critical.

Question 28: Which type of radiation is MOST penetrating and requires lead or thick concrete for shielding?

Alpha (α) radiation
Beta (β) radiation
Gamma (γ) radiation (Correct answer)
Ultraviolet radiation

Correct answer: Gamma (γ) radiation

Gamma radiation consists of high-energy electromagnetic photons with no mass or charge, making them the most penetrating form of ionizing radiation.

Ionizing radiation penetration: Alpha particles (α): He-2 nuclei (2 protons + 2 neutrons), large, +2 charge, low speed; stopped by paper, skin, or a few centimeters of air; most ionizing per unit path but least penetrating; dangerous if inhaled/ingested. Beta particles (β): electrons or positrons; moderate penetration; stopped by aluminum foil (few mm) or glass. Gamma rays (γ): high-energy electromagnetic photons; no mass, no charge; most penetrating; require lead or thick concrete/water for adequate shielding. Medical applications: Gamma rays are used in radiotherapy (destroy cancer cells), diagnostic PET scans, and sterilization of medical equipment.

Question 29: What is the term for the amount of a substance measured in moles per liter of solution?

Molality
Molarity (Correct answer)
Osmolarity
Normality

Correct answer: Molarity

Molarity (M) is defined as the number of moles of solute per liter of solution, expressed as mol/L or M.

Concentration measurements: Molarity (M) = moles of solute / liters of solution (mol/L) — the most commonly used concentration unit in chemistry; changes with temperature (volume changes). Molality (m) = moles of solute / kilograms of solvent (mol/kg) — does not change with temperature. Osmolarity = osmoles of solute per liter of solution — used in physiology to describe osmotic pressure (e.g., blood osmolarity ~285–295 mOsm/L). Normality (N) = equivalents of solute per liter — used in acid-base chemistry. In healthcare: IV solution concentrations are often expressed as percent (g/100 mL) or mEq/L (milliequivalents per liter).

Question 30: What is the term for the energy stored in an object due to its position or configuration?

Kinetic energy
Thermal energy
Potential energy (Correct answer)
Chemical energy

Correct answer: Potential energy

Potential energy is stored energy based on an object's position (gravitational PE), configuration (elastic PE), or chemical structure (chemical PE).

Types of energy: Kinetic energy — energy of motion (KE = ½mv²); increases with mass and speed. Potential energy — stored energy based on position or configuration: Gravitational PE (PE = mgh; depends on mass, gravity, height), Elastic PE (compressed/stretched springs), Chemical PE (energy stored in molecular bonds, released in chemical reactions). Energy conservation: PE + KE = constant (in absence of friction). In the body: glucose has chemical PE that is released during cellular respiration, converted to ATP (chemical PE) and ultimately to mechanical energy (muscle contraction) and heat.

Question 31: Which of the following correctly describes oxidation in a chemical reaction?

The gain of electrons by an atom or molecule
The loss of electrons by an atom or molecule (Correct answer)
The addition of oxygen to a reaction vessel
The removal of hydrogen gas from a compound

Correct answer: The loss of electrons by an atom or molecule

Oxidation is defined as the loss of electrons by an atom or molecule (remember OIL — Oxidation Is Loss). This often (but not always) involves gaining oxygen or losing hydrogen.

Redox (reduction-oxidation) reactions involve electron transfer: Oxidation = loss of electrons (the oxidized species loses electrons; its oxidation state increases). Reduction = gain of electrons (the reduced species gains electrons; its oxidation state decreases). Memory aid: OIL RIG (Oxidation Is Loss, Reduction Is Gain). In biological systems: cellular respiration involves oxidation of glucose (C₆H₁₂O₆ — carbon is oxidized, losing electrons to oxygen). Antioxidants (vitamins C and E) prevent oxidative damage by donating electrons to reactive oxygen species (free radicals), preventing cellular damage. Corrosion (rusting) is also an oxidation process.

Question 32: Which of the following is true about isotopes of the same element?

They have different numbers of protons but the same number of neutrons
They have the same number of protons but different numbers of neutrons (Correct answer)
They have different numbers of electrons and therefore different chemical properties
They are always radioactive

Correct answer: They have the same number of protons but different numbers of neutrons

Isotopes are atoms of the same element (same atomic number = same protons) that have different numbers of neutrons, giving them different mass numbers but nearly identical chemical behavior.

Isotopes have: Same number of protons (same element, same atomic number); Same number of electrons in neutral atoms (same chemical properties); Different numbers of neutrons (different mass numbers). Examples: Carbon-12 (6p, 6n) and Carbon-14 (6p, 8n) — both are carbon. Hydrogen isotopes: Protium (1p, 0n), Deuterium (1p, 1n), Tritium (1p, 2n). Medical uses: Radioactive isotopes (radioisotopes) are used in diagnostics (technetium-99m, iodine-131 for thyroid imaging) and therapy (radiation treatment). Carbon-14 is used in radiocarbon dating. Stable isotopes are non-radioactive and have virtually identical chemistry.

Question 33: When salt (NaCl) dissolves in water, what type of interaction occurs between the water molecules and the ions?

Covalent bond formation between water and NaCl
Ion-dipole interactions between polar water molecules and Na⁺ and Cl⁻ ions (Correct answer)
Hydrogen bonding between NaCl and water
London dispersion forces between the ions and water

Correct answer: Ion-dipole interactions between polar water molecules and Na⁺ and Cl⁻ ions

Polar water molecules orient their partial charges (δ⁻ oxygen near Na⁺, δ⁺ hydrogens near Cl⁻) to surround and stabilize the ions through ion-dipole interactions, enabling dissolution.

When NaCl dissolves in water: The ionic lattice is broken apart because the energy released by ion-dipole interactions between water molecules and ions compensates for the lattice energy. The partial negative charge (δ⁻) on water's oxygen is attracted to Na⁺ (cation), and the partial positive charge (δ⁺) on water's hydrogens is attracted to Cl⁻ (anion). Water molecules surround and stabilize each ion through hydration — this is called solvation. This is why polar solvents ('like dissolves like') dissolve ionic compounds. Nonpolar solvents like oil cannot interact with ions and cannot dissolve NaCl.

Question 34: A patient's blood sample is found to have a pH of 7.28. This condition is called:

Alkalosis
Acidosis (Correct answer)
Neutralization
Hypoxia

Correct answer: Acidosis

Normal blood pH is 7.35–7.45. A pH of 7.28 is below normal, indicating acidosis — too much acid (H⁺) or too little bicarbonate in the blood.

Blood pH homeostasis: Normal range 7.35–7.45 (slightly alkaline). Acidosis: pH < 7.35 (too much acid). Respiratory acidosis: CO₂ retention (hypoventilation) → more carbonic acid → H⁺ ↑. Metabolic acidosis: excess lactic acid (sepsis, diabetic ketoacidosis, renal failure). Alkalosis: pH > 7.45 (too little acid). Respiratory alkalosis: hyperventilation → CO₂ blown off → less carbonic acid. Metabolic alkalosis: excess vomiting (loss of HCl), excess antacids. pH 7.28 is a moderately severe metabolic or respiratory acidosis requiring clinical intervention. Extreme acidosis (<7.0) or alkalosis (>7.7) is life-threatening.

Question 35: What is the relationship between pressure and volume of a gas at constant temperature, as described by Boyle's Law?

Pressure and volume are directly proportional (P ∝ V)
Pressure and volume are inversely proportional (P ∝ 1/V) (Correct answer)
Pressure and volume are unrelated at constant temperature
Pressure doubles when volume doubles

Correct answer: Pressure and volume are inversely proportional (P ∝ 1/V)

Boyle's Law states that at constant temperature, pressure and volume of a gas are inversely proportional: as pressure increases, volume decreases (P₁V₁ = P₂V₂).

Boyle's Law: P₁V₁ = P₂V₂ (at constant temperature). Pressure and volume are inversely proportional: if volume doubles, pressure halves; if volume halves, pressure doubles. Application to breathing: During inhalation, the diaphragm contracts and chest cavity expands (volume increases) → intrapulmonary pressure drops below atmospheric pressure → air flows in. During exhalation, volume decreases → pressure increases above atmospheric → air flows out. This is a direct application of Boyle's Law in respiratory physiology. Charles's Law relates volume and temperature at constant pressure (directly proportional).

Question 36: Which of the following correctly describes the process of neutralization?

An acid donates electrons to a base
A reaction between an acid and a base that produces a salt and water (Correct answer)
A reaction where a neutral solution is made acidic
A process where hydrogen gas is released

Correct answer: A reaction between an acid and a base that produces a salt and water

Neutralization occurs when an acid and a base react together to form a salt and water. For example: HCl + NaOH → NaCl + H₂O.

Neutralization: Acid + Base → Salt + Water. The H⁺ from the acid combines with the OH⁻ from the base to form water (H⁺ + OH⁻ → H₂O). The remaining ions form a salt. Example: HCl (acid) + NaOH (base) → NaCl (salt) + H₂O. The resulting solution may be neutral (pH 7), weakly acidic, or weakly basic depending on the relative strengths of the acid and base. Clinical applications: antacids (calcium carbonate, magnesium hydroxide) neutralize excess stomach acid (HCl); bicarbonate administration neutralizes blood acidosis; buffering systems use partial neutralization to resist pH changes.

TEAS Science: Chemistry and Physical Science 1

What is the pH of a neutral solution at 25°C?

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